Github user zentol commented on the issue:
https://github.com/apache/flink/pull/2210
Calling close() isn't necessary since no metric should ever be registered
directly on the IOMetricGroup. This group is supposed to only contain
pre-defined metrics that can be accessed from multiple places. These metrics
are registered on the TaskMetricGroup, and thus cleaned up.
A proper fix would be to override the addMetric() method to throw an
exception when that is done, or to refer registration to the TaskMetricGroup.
Addendum for clarification: TaskMetrics aren't technically cleaned up at
the end of the job, but when no task for a given job runs on a TM.
Given the current usage of the IOMetricGroup i sincerely doubt that is
caused an actual issue, and thus would like you provide more information on the
issue you faced.
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